This invention relates to semiconductor devices, and more specifically relates to a novel device in which a plurality of die, which may be of diverse size and of diverse junction pattern, are fixed to a common die pad and another die is fixed to another die pad, all being disposed within a common package or housing.
Numerous electrical circuits, for example, DC to DC converters, synchronous converters, and the like require a number of semiconductor components such as MOSFETs and Schottky diodes. These circuits are frequently used in portable electronics apparatus and their components are commonly separately housed and must be individually mounted on a support board. The separately housed parts take up board space. Further, each part generates heat and, if near other components, such as microprocessors, can interfere with the operation of the microprocessor.
Referring to FIG. 1, there is shown a conventional buck converter circuit, sometimes known as a step down converter, which is commonly used to reduce the voltage delivered to integrated circuits and processors on a circuit board of a portable electronic device or the like. For example, the circuit might be used to reduce an input voltage of 12 volts DC to 5 volts DC (or 3.3 or 1.5 volts DC in some cases) to drive an integrated circuit or other load (not shown).
The circuit of FIG. 1 is well known and uses an N-channel MOSFET 10 for the switching function under the control of a suitable control circuit 11 connected to the MOSFET gate G. A Schottky diode 12 has its cathode connected to the drain D of MOSFET 10 and is used to permit output current recirculation into inductor 13 and capacitor 14 when the MOSFET 10, usually operated with pulse frequency modulation control, is off.
U.S. Pat. No. 5,814,884 discloses a package in which a MOSFET and Schottky diode are mounted on a common die pad in order to reduce board space, parts count, and costs.
It would be desirable to reduce the board space required by plural semiconductor devices and to reduce part count and assembly costs in such power converters and other power subsystems for high-density applications.
In accordance with one aspect of the invention a semiconductor device includes: at least first, second, and third semiconductor die, each having opposing surfaces which contain respective electrodes; a conductive lead frame including first and second separate die pad areas, the first and second semiconductor die being disposed on the first die pad, and the third semiconductor die being disposed on the second die pad; a first plurality of pins being integral with and extending from one edge of the first die pad; a second plurality of pins being integral with and extending from one edge of the second die pad; a third plurality of pins being separated from one another and from the first and second dice pads; a first plurality of bonding wires connecting one surface of the first semiconductor die to at least one of the third plurality of pins; a second plurality of bonding wires connecting one surface of the third semiconductor die to at least another one of the third plurality of pins; and a housing for encapsulating the lead frame, semiconductor dice, and bonding wires, the first, second and third pluralities of pins extending beyond a periphery of the housing for external connection.
The housing and first, second, and third pluralities of pins may conform to an SO-8 package standard. The first and second pluralities of pins may be disposed along a common edge of the housing. Preferably, the third plurality of pins is disposed along an opposite common edge of the housing.
According to another aspect of the invention, the first and second dice are MOSFET die, each having a source, drain and gate electrode; the surfaces of the first and second MOSFET die in contact with the respective first and second die pad areas are the drain electrodes; and the respective source and gate electrodes of the first and second MOSFET die are connected to respective ones of the third plurality of pins.
Preferably, the second semiconductor die is a Schottky diode die, the opposite surface of the second semiconductor die including a cathode electrode of the Schottky diode which is coupled to the first die pad area such that the cathode electrode of the Schottky diode is electrically connected to the drain electrode of the first MOSFET die and to the first plurality of pins, the opposite surface of the Schottky diode die comprising an anode electrode. Preferably, the anode electrode of the Schottky diode die is coupled via bonding wires to the source electrode of the first MOSFET die.
In accordance with a further improvement of the invention, a single source lead connected to a separate pin acts as a Kelvin contact for the control MOSFET; and power connections between the die are made internally of the housing, rather that at the pin outs, reducing noise and simplifying board mounting.